The Weapon Plus Program was a clandestine organization determined to produce the ultimate super-soldier or superhuman operatives. Retroactively adopting Project: Rebirth and Abraham Erskine's success with Captain America as "Weapon One", Weapon Plus followed up with a series of experiments over several decades using both voluntary and involuntary test subjects. Their research covered areas of cybernetics, drug therapy, genetic manipulation, nanotechnology, even time manipulation, as well as memory implants and behavioral modification to maintain control of their weapons. The infamous Weapon X Program was the 10th project for Weapon Plus, but broke free from the parent organization to conduct independent testing under the Professor.
According to one document, the earliest Weapon Plus experiments were conducted on animals and ethnic minorities before proceeding into mutant experiments. Although the Skinless Man was identified as Weapon III, it's possible that is from a separate numbering system from the Weapon Plus UK series, as he doesn't fit into the above categories.
Weapon I - Project: Rebirth - Captain America
Weapon II - Brute Force
Weapon III - Skinless Man
Weapon IV - Project: Sulphur - Man-Thing, Man-Slaughter
Weapon V - Project: Venom
Weapon VI - Project: Power - Luke Cage
Weapon VII - Project: Homegrown - Nuke
Weapon VIII - ????
Weapon IX - Project: Psyche - Reportedly connected to Typhoid Mary
Weapon X - Wolverine
Weapon XI - ????
Weapon XII - Huntsman
Weapon XIII - Fantomex
Weapon XIV - Stepford Cuckoos
Weapon XV - Ultimaton
Weapon XVI - Allgod
Weapon XXX - ????